Histopathological and hematological findings in myeloid leukemia induced by a new feline leukemia virus isolate

Overview of Bone Marrow Aspiration from 120 Cats in Different Hematological Conditions

Bone marrow (BM) evaluation is highly important for the diagnosis of numerous hematological alterations in animals, especially cats, given their greater propensity for hematopoietic changes associated with retrovirus infections. This study aims to describe the main aspects of the BM of cats with different hematological conditions, comparing with reference intervals established from animals without hematological alterations and also with a previously established reference interval. To do so, we evaluated full blood and BM samples from 120 cats with no abnormalities on physical examination, negative for FeLV and FIV. Hemograms were performed from automated total cell and platelet and leukocyte differential counts in blood smears. BM samples were placed in Petri dishes; medullary spicules were selected to make up to eight cytological slides stained by the May-Grunwald-Giemsa technique, which were subjected to quantitative and cellular morphology evaluations. The cats were predominantly young, 64.2% female and 35.8% male. The average number of medullary spicules in samples was 13.7%, and density was 44%. In the BM quantitative analysis, prorubricytes and rubriblasts had higher quantities than the recommended one for all cats with or without hematological alterations. In all groups, lymphocytes were decreased, and cats with lymphocytosis were closest to the reference range, showing flame cells and Mott cells. The reference interval for the bone marrow cell count obtained from the samples in this work differs from previously established data, leading to different interpretations of the patient's BM condition, according to the cell population observed and the reference interval used. This divergence strongly emphasizes the need to correlate clinical, epidemiological, hematological, and bone marrow data of each patient for a better understanding of the patient's condition. The popularization of BM assessment is essential so that more reliable reference intervals can be established according to the population served by each pathologist and clinical laboratory.

Phylogenetic identification of feline leukemia virus A and B in cats with progressive infection developing into lymphoma and leukemia

To date, only a few studies have examined the impacts of feline leukemia virus (FeLV) subgroups on disease development in spontaneously infected cats. The present study identified FeLV-A and FeLV-B subgroups in cats with lymphoma and leukemia and explored the phylogenetic relationships of env sequences. Twenty-six cats with lymphoma (n=16) or leukemia (n=10) were selected. FeLV p27 antigen positivity was determined using ELISA, and proviral DNA in blood samples was detected using nested PCR. Positive animals in both tests were classified as cases of FeLV progressive infection and subjected to a second nested PCR for env amplification and subgroup determination. Six samples of FeLV-A and five samples of FeLV-B were sequenced using the Sanger method, and the results were used to build a phylogenetic tree and estimate evolutionary divergence. Among cats with lymphoma, 68.8% carried FeLV-AB and 31.2% FeLV-A. Among cats with leukemia, 70% carried FeLV-AB and 30% FeLV-A. Regarding cat characteristics, 50% were young, 30.8% young adults, and 19.2% adults; 88.5% were mixed-breed and 11.5% pure breed; and 42.3% were males and 57.7% were females. Among lymphomas, 62.5% were mediastinal, 31.3% multicentric, and 6.3% extranodal. Regarding histological classification, lymphoblastic and small non-cleaved-cell lymphomas were the most frequently detected. Among leukemia cases, 30% were acute lymphoid, 30% chronic myeloid, and 40% acute myeloid. Phylogenetic analysis showed that FeLV-A SC sequences were closely related to the Arena, Glasgow-1, and FeLV-FAIDS variants. Meanwhile, FeLV-B SC sequences were divergent from one another but similar to the endogenous FELV env gene (enFeLV). In conclusion, FeLV-AB is prevalent in cats with lymphoma and leukemia, highlighting the genetic diversity involved in the pathogenesis of these neoplasms in Brazil.

The feline blood film

Practical relevance: Many veterinary practices have invested in quality automated hematology instruments for use in-house. However, regardless of their specific choice of analyzer, there are important hematology findings that can only be determined by microscopic examination of stained blood films. For this reason, and also for the purpose of quality control for the analyzer, a quick blood film review should be performed alongside every automated complete blood count. Even those practices that submit their blood samples to outside diagnostic laboratories for evaluation, still require the capability to examine stained blood films in emergency situations. Series outline: This is the second of a two-part article series that aims to familiarize the practitioner with normal findings on feline blood films, with a particular focus on unique features in the cat, as well as to assist with interpretation of common abnormalities. Part 2 focuses on the morphology of feline leukocytes and platelets in health and disease. Evidence base: The information and guidance offered is based on the published literature and the author's own extensive clinical pathology research.

Spontaneous mediastinal myeloid sarcoma in a common marmoset (Callithrix jacchus) and review of the veterinary literature

BACKGROUND

Myeloid sarcoma is a rare manifestation of myeloproliferative disorder defined as an extramedullary mass composed of myeloid precursor cells. A 9-month old, female, common marmoset (Callithrix jacchus) had increased respiratory effort.

METHODS

A complete necropsy with histology and immunohistochemistry was performed.

RESULTS

The thymus was replaced by a firm, gray-tan mass with a faint green tint, filling over 50% of the thoracic cavity. Sheets of granulocytes, lymphoid cells, nucleated erythrocytes, megakaryocytes, and hematopoietic precursors of indeterminate cell lineage replaced the thymus, perithymic connective tissue, mediastinal adipose tissues, epicardium, and much of the myocardium. The cells demonstrated diffuse strong cytoplasmic immunoreactivity for lysozyme, and strong, multifocal membranous immunoreactivity for CD117.

CONCLUSION

We report the first case of a myeloid sarcoma in a common marmoset (C. jacchus), similar to reported human cases of mediastinal myeloid sarcoma, and present a review of myeloproliferative diseases from the veterinary literature.

Pelger-Huët anomaly in two related mixed-breed dogs

A 6-month-old male mixed-breed dog weighing 12.6 kg weight was presented for evaluation of a subcutaneous nodule on the dorsum. The medical history indicated trimethoprim-sulfamethoxazole treatment 2 months before presentation at the veterinary hospital. The initial complete blood cell count (CBC) results included an apparent left shift. Microscopic examination of a blood smear (Panoptic stain) revealed granulocytes with hyposegmented nuclei, coarse mature chromatin, and a nuclear shape varying from round to bilobed (pince-nez) or slightly indented. Occasional neutrophils and eosinophils had typical segmentation of nuclei. Abnormalities were not present in limited serum biochemical testing. The CBC was repeated 17 and 120 days later, and the results were similar to those observed in the first examination. The parents of the patient were located, and a CBC was performed on both animals. The dam, but not the sire, had nuclear hyposegmentation of granulocytes, confirming the diagnosis of Pelger-Huët anomaly.

A cat with acute myeloblastic leukemia without maturation (M1) treated with combination chemotherapy

A 2-year-old domestic shorthair cat was presented to us with decreased activity and anorexia. Hematologic findings revealed a mild non-regenerative anemia, thrombocytopenia, and leukocytosis with an increase in blast cells. Bone marrow aspirates also revealed a marked increase of blasts. The blastic cells were shown to be positive for peroxidase. Acute myeloblastic leukemia without maturation (M1) was diagnosed according to the FAB classification. Chemotherapy was initiated with cyclophosphamide, vincristine, prednisolone, and cytosine arabinoside. The cat responded partially. In total, the cats were given 7 blood transfusions. The cat died 14 weeks after first being presented to us.

Acute myeloid leukemia with basophilic differentiation (AML, M-2B) in a cat

A 4-year-old, neutered male Domestic Shorthair cat with a history of depression, anorexia, and weight loss was diagnosed with acute myelogenous leukemia (AML). The cat tested positive by both the feline immunodeficiency virus antibody test and feline leukemia virus enzyme-linked immunosorbent assay test. Results of cytochemical stains on peripheral blood and bone marrow specimens indicated acute myeloid leukemia with unusual basophilic differentiation (AML, M-2B).

Effect of preexisting FeLV infection or FeLV and feline immunodeficiency virus coinfection on pathogenicity of the small variant of Haemobartonella felis in cats

OBJECTIVE

To investigate the effects of preexisting FeLV infection or FeLV and feline immunodeficiency (FIV) coinfection on the pathogenicity of the small variant of Haemobartonella felis (Hfsm, California variant) in cats.

ANIMALS

20 FeLV infected, 5 FeLV-FIV coinfected, and 19 retrovirus-free cats.

PROCEDURES

A client-owned cat, coinfected with FeLV and Hfsm, was the source for Hfsm. Inoculum 1 (FeLV free) was obtained by passage of source Hfsm through 4 FeLV-resistant cats. Inoculum 2 was obtained by further passage of Hfsm (inoculum 1) through 2 specific pathogen-free cats.

RESULTS

A mild-to-moderate anemia started 21 days after inoculation, with its nadir occurring at 35 to 42 days after inoculation. Infection with Hfsm induced greater decrease in hemoglobin concentration in FeLV infected cats, compared with retrovirus free cats. Reticulocytosis, macrocytosis, and polychromasia of erythrocytes developed in anemic cats regardless of retrovirus infection status. Mean neutrophil counts decreased during the hemolytic episode. For most cats, the anemia was transient. Four FeLV infected cats, 1 of which was also FIV infected, developed fatal FeLV-associated myeloproliferative diseases. Of the surviving cats, 8 died over the next 24 months from other FeLV-related diseases. Hemolysis did not recur after the initial episode. Inoculum 1 induced more severe anemia than inoculum 2.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results support the clinical observation that cats coinfected with FeLV and H felis develop more severe anemia than cats infected with H felis alone. Infection with Hfsm may induce myeloproliferative disease in FeLV infected cats. The small variant of H felis may lose pathogenicity by passage through FeLV-free cats.

Clinical and laboratory evaluation of the safety of a bioartificial liver assist device for potential transmission of porcine endogenous retrovirus

BACKGROUND

The potential risk of transmission of porcine endogenous retroviruses (PERV) from xenogeneic donors into humans has been widely debated. Because we were involved in a phase I/II clinical trial using a bioartificial liver support system (BLSS), we proceeded to evaluate the biosafety of this device.

MATERIALS AND METHODS

The system being evaluated contains primary porcine hepatocytes freshly isolated from pathogen-free, purpose-raised herd. Isolated hepatocytes were installed in the shell, which is separated by a semipermeable membrane (100-kD nominal cutoff) from the lumen through which the patients' whole blood is circulated. Both before and at defined intervals posthemoperfusion, patients' blood was obtained for screening. Additionally, effluent collected from a clinical bioreactor was analyzed. The presence of viral particles was estimated by reverse transcriptase-polymerase chain reaction (RT-PCR) and RT assays. For the detection of pig genomic and mitochondrial DNA, sequence-specific PCR (SS-PCR) was used. Finally, the presence of infectious viral particles in the samples was ascertained by exposure to the PERV-susceptible human cell line HEK-293.

RESULTS

PERV transcripts, RT activity, and infectious PERV particles were not detected in the luminal effluent of a bioreactor. Culture supernatant from untreated control or mitogen-treated porcine hepatocytes (cleared of cellular debris) also failed to infect HEK-293 cell lines. Finally, RT-PCR, SS-PCR, and PERV-specific RT assay detected no PERV infection in the blood samples obtained from five study patients both before and at various times post-hemoperfusion.

CONCLUSION

Although longer patient follow-up is required and mandated to unequivocally establish the biosafety of this device and related bioartificial organ systems, these analyses support the conclusion that when used under standard operational conditions, the BLSS is safe.

Infection by porcine endogenous retrovirus after islet xenotransplantation in SCID mice

Animal donors such as pigs could provide an alternative source of organs for transplantation. However, the promise of xenotransplantation is offset by the possible public health risk of a cross-species infection. All pigs contain several copies of porcine endogenous retroviruses (PERV), and at least three variants of PERV can infect human cell lines in vitro in co-culture, infectivity and pseudotyping experiments. Thus, if xenotransplantation of pig tissues results in PERV viral replication, there is a risk of spreading and adaptation of this retrovirus to the human host. C-type retroviruses related to PERV are associated with malignancies of haematopoietic lineage cells in their natural hosts. Here we show that pig pancreatic islets produce PERV and can infect human cells in culture. After transplantation into NOD/SCID (non-obese diabetic, severe combined immunodeficiency) mice, we detect ongoing viral expression and several tissue compartments become infected. This is the first evidence that PERV is transcriptionally active and infectious cross-species in vivo after transplantation of pig tissues. These results show that a concern for PERV infection risk associated with pig islet xenotransplantation in immunosuppressed human patients may be justified.

Myelopoiesis and myeloproliferative disorders

Myeloid cells arise from a common stem cell whose development is regulated by stimulatory and inhibitory growth factors. Pluripotential hematopoietic stem cells are most influenced by IL-3, GM-CSF, and stem cell factor while committed progenitor cells are regulated by variable concentrations of GM-CSF, G-CSF, M-CSF, IL-5, Epo, and Tpo. As a result of their common origin, a key point to remember about myeloproliferative disorders is the involvement of multiple cell lines in dysplastic and neoplastic conditions. Dysplastic changes may signal early neoplastic changes with cases progressing to acute leukemia. Myelodysplastic syndrome (MDS) is associated with anemia or multiple cytopenias, normal to hypercellular bone marrow, ineffective hematopoiesis, and less than 30% blast cells of all nucleated cells in the bone marrow. Chronic myeloid leukemias also have less than 30% blast cells of all nucleated cells in the bone marrow and are distinguished from MDS by elevated cell counts of one or more cell lines with mature forms predominating. Acute myeloid leukemias, often the end result of all myeloproliferative disorders, are recognized by equal or greater 30% blast cells of all nucleated cells in the bone marrow. Additional diagnostic information from cytochemical stains, immunohistochemical staining, and cytogenetic analysis can influence the final diagnosis when morphology alone is equivocal. In conclusion, prognosis and response to treatment are best determined by application of a uniform set of standards in evaluating hematolymphatic neoplasia. Critical to diagnosis are complete blood and bone marrow evaluations including observation for dysplastic changes and blast cell quantitation. In addition, evidence for tissue infiltration identified through cytologic or histologic evaluations of lymph node, spleen, or liver is recommended.

Haematological disorders associated with feline retrovirus infections

Feline oncornavirus and lentivirus infections have provided useful models to characterize the virus and host cell factors involved in a variety of marrow suppressive disorders and haematological malignancies. Exciting recent progress has been made in the characterization of the viral genotypic features involved in FeLV-associated diseases. Molecular studies have clearly defined the causal role of variant FeLV env gene determinants in two disorders: the T-lymphocyte cytopathicity and the clinical acute immunosuppression induced by the FeLV-FAIDS variant and the pure red cell aplasia induced by FeLV-C/Sarma. Variant or enFeLV env sequences also appear to play a role in FeLV-associated lymphomas. Additional studies are required to determine the host cell processes that are perturbed by these variant env gene products. In the case of the FeLV-FAIDS variant, the aberrant env gene products appear to impair superinfection interference, resulting in accumulation of unintegrated viral DNA and cell death. In other cases it is likely that the viral env proteins interact with host products that are important in cell viability and/or proliferation. Understanding of these mechanisms will therefore provide insights to factors involved in normal lymphohaematopoiesis. Similarly, studies of FeLV-induced haematological neoplasms should reveal recombination or rearrangement events involving as yet unidentified host gene sequences that encode products involved in normal cell growth regulation. These sequences may include novel protoncogenes or sequences homologous to genes implicated in human haematological malignancies. The haematological consequences of FIV are quite similar to those associated with HIV. As with HIV, FIV does not appear to directly infect myeloid or erythroid precursors, and the mechanisms of marrow suppression likely involve virus, viral antigen, and/or infected accessory cells in the marrow microenvironment. Studies using in vitro experimental models are required to define the effects of each of these microenvironmental elements on haematopoietic progenitors. As little is known about the molecular mechanisms of FIV pathogenesis, additional studies of disease-inducing FIV strains are needed to identify the genotypic features that correlate with virulent phenotypic features. Finally, experimental FIV infection in cats provides the opportunity to correlate in vivo virological and haematological changes with in vitro observations in a large animal model that closely mimics HIV infection in man.

Feline retroviruses: a brief review

Representatives of all three retrovirus subfamilies are recognized in the cat: feline leukaemia virus (an Oncovirus), feline syncytium-forming virus (a Spumavirus) and feline immunodeficiency virus (a Lentivirus). Each of these is briefly reviewed.